Apparatus for treating and mixing particles

ABSTRACT

An apparatus for treating particles with a liquid and for subsequent thorough mixing of the treated particles. The mixer comprises upright, concentric, spaced inner and outer walls, a helical ribbon disposed between the walls and mounted for rotation about an upright axis, means for feeding treated particles to the bottom of the helical ribbon, and means for withdrawing the mixed, treated particles from the top of the ribbon. The inner wall at least partially defines a chamber wherein the particles are treated with a liquid. Augering of the treated particles upwardly along the rotating, helical ribbon provides thorough mixing.

United States Patent 1191 Weber Oct. 14, 1975 [54] APPARATUS FORTREATING AND MIXING 3,779,033 l2/l973 Swanson 222/241 PARTICLES PrimaryExaminerPeter Feldman l t A. W M [75] nven or a sg eber mneapohsAssistant ExammerJames A. N1egowsk1 Attorney, Agent, or Firm-H. DalePalmatier; James [73] Assignee: Gustafson, Inc., Hopkins, Minn. R H n[22] Filed: Jan. 17, 1974 21 Appl. No.: 434,033 [57] ABSIRACT Anapparatus for treating particles with a liquid and for subsequentthorough mixing of the treated parti- [52] 3 42825 45 cles. The mixercomprises upright, concentric, spaced I I2 11/04 inner and outer walls,a helical ribbon disposed beg 259 2 ?g tween the walls and mounted forrotation about an up- 1 3 right axis, means for feeding treatedparticles to the l 8 g l 2 24 3 bottom of the helical ribbon, and meansfor withdraw- 9 21 1 ing the mixed, treated particles from the top ofthe ribbon. The inner wall at least partially defines a [56] ReferencesCited chamber wherein the particles are treated with a liq- UNITEDSTATES PATENTS uid. Augering of the treated particles upwardly along2,517,456 8/1950 Wherrett 259/7 the rotating, helical ribbon provides.thorough mixing.

2,953,359 9/1960 Mau 2591s i 3,155,542 11/1964 Cordell et al. 118/303 14Chums 3 Drawmg Figures 11' {2 ll 1 II 12.5

a4 lllll 12.2 222 q q" l l 225m. 121 22 14 A 51- I "lllll 165 d? .2252a; .22 22.!

m1 1- I a2! APPARATUS FOR TREATING AND MIXING PARTICLES u BACKGROUND orTHE INVENTION Particles, particularly seeds, often are provided with acoating of a liquid such as a pesticide, the relative volumes ofparticles and liquids being carefully controlled. A convenient manner ofcoating seeds is to spray falling seeds with small droplets of liquidand thereafter thoroughly mixing the seeds so that the droplets ofliquid originally adhering to the seeds are spread over the entire seedsurface. In the past, this has required extremely thorough mixing, andlarge and bulky mixing apparatuses were designed to accomplish thispurpose. The seeds must be mixed thoroughly in order to completely coverthe seed surface with liquid, and yet the seeds must be handled gentlyto avoid seed damage. A unitary, portable, compact apparatus capable oftreating particles such as seeds with a liquid and thoroughly mixing thetreated particles is much to be desired.

BRIEF SUMMARY OF THE INVENTION The present invention relates to atreating and mixing apparatus for applying a liquid to falling particlesand for thoroughly mixing or agitating the particles so as to spread theliquid thoroughly over the surface of the particles. The mixer includesupright, concentric, spaced inner and outer walls, the inner wall atleast partially defining a chamber within which particles are contactedwith a liquid. A helical ribbon is disposed between the walls and ismounted for rotation about an upright axis of rotation. The mixerincludes means for feeding treated particles to the bottom of thehelical ribbon when the ribbon is rotating about its axis, and means forremoving the mixed particles from the top of the ribbon. Upon enteringthe bottom of the helical ribbon, the treated particles are augeredupwardly along the rotating helical ribbon to provide thorough mixingand distribution of liquid upon the particle surfaces.

DESCRIPTION OF THE DRAWING FIG. 1 is a perspective view of an apparatusof the invention;

FIG. 2 is a cross-sectional view of the apparatus of FIG. 1, taken alongline 22; and

FIG. 3 is a broken away, cross-sectional view taken along line 33 ofFIG. 2.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT The treating and mixingapparatus of the invention, designated generally as in FIG. 1, includesa conical hopper 12 into which seeds or other particles to be treatedare placed, and a compact housing 14 which houses the treating andmixing apparatus 'of the invention. The hopper 12 is supported above thehousing 14 by upright struts 14.1. Exteriorly of the housing 14 ismounted a power source such as electric motor 16 which is mechanicallycoupled to a drive shaft 16.1 through a belt and sheave system 16.2 andwhich in turn serves to drive certain rotating elements within thehousing, as will be subsequently explained, through belt and sheavearrangement 16.3 and 16.4

A vertical sleeve 18 is mounted by straps 18.1 to the inner surface ofthe hopper 12, the sleeve 18 having a stationary distributing cone 18.2at its lower end, the

upper surface of the cone converging upwardly such that seeds or otherparticles which are dropped through the hopper contact the upper surfaceof the cone and are distributed outwardly to fall as a curtain over theouter cone rim 18.3. A movable ring 12.1 slidably encompasses thenarrowed throat 12.2 of the hopper, the lower end of the ringconfronting the upper surface of the cone. The height of the ring 12.]above the cone is regulated by turning of a handle 12.3 locatedexteriorly of the housing 14, the handle operating to rotate a threadedshaft 12.4 to raise and lower support arms 12.5 connected by a harness12.6 to the ring 12.1. The ring serves to regulate the rate at whichparticles are delivered to the cone; as the ring is lowered toward thecone, the flow rate of particles is reduced.

A disc 20 is affixed to the end of a shaft 20.1 which in turn passesupwardly through the sleeve 18. A sheave 20.2, connected to the top ofthe shaft 20.1, is driven by the drive shaft 16.1 through the belt andsheave 16.3. A housing 20.3 for the belt and sheave 20.2 extendsinternally of the hopper 12 and is held in place by straps 20.4. Thedisc 20 is positioned directly beneath the cone 18.2 and is coaxial withthe cone. The disc may have radial serations 20.5, the purpose of whichwill be subsequently explained.

A fluid delivery tube 21 extends downwardly through the hopper l2 andpasses through the cone 18.2 into close proximity with the upper surfaceof the disc 20. The tube 21 is held in place by its passage through thedisc 20 and by a bracket 18.4 within the throat of the hopper. Fluid,such as a pesticide, is delivered to tube 21 in measured amounts from anexternal source (not shown). The liquid may be metered to the tube 21from a reservoir of liquid by means of a volumetric pump such as a gearpump or by other known measuring devices. The motor 16 causes the discto rapidly rotate about its axis, and liquid which is depositedon theupper surface of the disc near its connection with the shaft 20.1 ishurled outwardly by centrifugal force in the form of small dropletswhich contact the curtain of particles falling from the rim 18.3 of thedistributing cone. In the case of seeds, such as soy bean seeds, theliquid may be seen under magnification to be present on the surface ofthe seeds as small spatters or droplets, and it is the subsequent mixingaction which rubs one seed against another and thus spreads the liquidthoroughly and completely over the outer surface of the seeds. The powersource may be provided with a variable speed control so that the speedof the rotating disc may be varied as desired.

The cone and rotatingdisc are housed within a pair of concentric,spaced, upright, cylindrical walls 22 and 24, as shown in FIG. 2. Theouter wall 22 arises from the periphery of a circular floor 26 to form adrumshaped container, and the inner surfaces of the outer wall 22 andfloor 26 are provided with a low friction plastic surface 22.1, 22.6,such as Teflon. A shaft 28 passes upwardly through a central aperture inthe floor, and is provided with an exterior sheave 28.1 which isrotatably driven by the belt and sheave system 16.4. The shaft 28 risesonly a short distance above the surface of the floor and is providedwith a slot in which is carried an elongated paddle 30 of generallyrectangular cross section. The ends 30.1 of the paddle are bent as shownin FIG. 3 to define a generally planar superior surface oriented at anobtuse angle with respect to the floor 26. The paddle is attached, as bywelding, to the lower edge 24.1 of the inner wall 24 and serves tosupport the inner wall spaced above the top surface of the floor. Crossstruts 30.2 are attached to the paddle 30 and extend outwardly from thepaddle for attachment to points 24.2 about the lower periphery of theinner wall 24. The paddle 30, and cross struts 30.2, support the innerwall in spaced relationship above the floor and rotate the inner wallabout the axis of the cone and disc when the shaft 28 is rotated by themotor 16. The bottom edge of the paddle 30 is in contact with andscrapes or sweeps the upper surface of the floor as the paddle isrotated, thereby urging fallen seeds or other particles outwardlybeneath the upwardly spaced lower edge 24.1 of the inner wall 24.

One or more helical ribbons 32 are rigidly attached, as be welding, tothe outer surface of the inner wall 24, as depicted in FIG. 2, andextend laterally outwardly into sliding contact with the low frictionsurface 22.1 of the outer wall 22. Although one or more helical ribbonsmay be thus employed, good results have been obtained with two helicalribbons, helically interlaced about the inner wall. Each helical ribbonat its bottom end contacts a bent end of the paddle 30, the superiorsurface of the helical ribbon at its lower end merging into the superiorsurface of the bent paddle end such that seeds or other particles whichare swept outwardly across the floor towards the periphery of the outerwall are cammed upwardly by the bent paddle ends to enter the helicalpassages defined by the helical ribbons. The helical ribbons rotate withthe inner wall 24 and the paddle 30, and seeds or other particles areaugered upwardly through the helical passages, movement of the particlesin this fashion giving rise to thorough rubbing and mixing betweenparticles so as to uniformly coat each particle with the liquid. Anopening 22.2 is provided at the upper end of the outer wall 22 so thatparticles which have reached the top-most surface of the helical ribbonsmay pour outwardly in the direction shown by arrow 22.3 into the spacebetween the housing 14 and the outer wall 22, for subsequent collectionin a suitable container. Each helical ribbon is provided at its upperend with an upright deflection plate 32.1 oriented at an acute angle toa plane passing through the plate and through the axis of rotation ofthe shaft 28 so as to urge particles advancing upwardly along thesuperior surface of the upper end of the helical ribbon in an outwardlydirection so that the particles exit through the opening 22.2 in theouter wall 22.

An annular cover 34 having an inverted U configuration fits over theupper edges of the inner and outer walls 24 and 22 to cover the annularspace between these walls and to prevent dust or the like from escap- Asnoted above, the disc may have a radially serated edge as shown in FIG.2. The purpose of the serated edge is to increase the surface area ofthe disc across which liquid is transported by centrifugal force andalso to expand the vertical distance within the chamber in which liquiddroplets are hurled outwardly from the periphery of the disc. Liquidwhich departs from the disc at a seration peak will travel in agenerally horizontal plane outwardly. Liquid departing from the disc ata valley portion of the serated edge will be hurled outwardly in agenerally horizontal plane slightly lower than the first plane. Thus,the vertical distance in which outwardly hurled liquid droplets maycontact the falling curtain of particles increases with increasingseration depth, and a greater proportion of the falling particles maythus be contacted by the outwardly hurled liquid droplets. The disc maybe rotated at any convenient speed which is sufficiently high to givethe desired results. For a disc approximately 6 inches in diameter, asuitable speed for liquid having a viscosity on the order of that ofwater is 2,800 revolutions per minute. The speed may be adjustedupwardly, or downwardly, as desired, and it has been found that foroptimum results, different speed settings within a range of from about1,500-2,8OO revolutions per minute are desired for liquidsof differentviscosities. It has generally also been found that the ability of theliquid to contact a large proportion of the falling particles isincreased as the liquid flow rate to the spinning disc is decreasedwithin limits. High liquid flow rates to the spinning disc result inlarge droplets of liquid being hurled from the disc. As the flow rate isreduced. the droplet size is likewise reduced. For optimum results, itis desired that the spinning disc form an outwardly directed, mist-likespray of droplets. Again, the droplet size is also dependent upon thespeed of the spinning disc, and more precisely upon the linear velocityof the periphery of the disc.

The rotational speed of the inner wall 24 and the attachedhelical'ribbons is of importance to proper operation of the apparatus ofthe invention. At least some difference is required between therotational speed of the helical ribbons and the rotational speed, ifany, imparted'to the seeds or other particles in order for the ribbonsto auger the particles upwardly. If the rotational speed of the helicalribbons is too low, the seeds or other particles will become seated onthe superior surfaces of the ribbons and will rotate with the ribbons,the helical passages eventually becoming obstructed withparticles. Ingeneral, higher rotational speeds are required for smaller particles.Because of the intimate contact which occurs between the walls of thehelical passages and the particles passing through these passages, theparticles will normally acquire some angular momentum by the time theyreach the top-most. ends of the helical ribbons. It is required that therotational speed of the helical ribbons be such as to provide at leastsome, though varying, differential between the angular velocity of theseeds and the ribbons as the seeds are augered upwardly through thehelical passages. For an apparatus of the invention having twointerlaced helical ribbons each making approximately six revolutionsabout the periphery of the inner wall, the outer and inner diameters ofthe inner and outer walls respectively being 12 and 18 inches, anangular speed of 250 revolutions per minute has yielded good resultswith soy bean seeds.

If desired, an upright, stationary scraper bar may be oriented againstthe inner surface of the inner wall 24 so that as the wall rotatesduring operation of the apparatus, seeds or other particles which mayadhere to the inner wall are scraped from the wall and fall to the floor26. It will further be understood that the rotational speed of the shaft28 driving the helical ribbons may be widely varied with respect to therotational speed of the shaft 20.1 driving the spinning disc 20, sincethe speed of the disc 20 is largely dependent upon the viscosity andquantity of liquid which is dispensed through the tube 22, as notedabove, whereas the rotational speed required for the helical ribbons islargely dependant upon the size and density of the treated particles. Itwill be understood that other devices, such as liquid spray nozzles orthe like may be employed for treating particles with liquid prior tomixing the particles.

While I have described a preferred embodiment of the present invention,it should be understood that various changes, adaptations, andmodifications may be made therein without departing from the spirit ofthe invention and the scope of the appended claims.

What is claimed is:

1. In combination with a treating apparatus for applying a liquid tofalling particles',a mixer for mixingthe treated particles, the mixerincluding upright, concentric, spaced inner and outer walls defining anannular space therebetween, the inner wall defining walls of a centralparticle-treating chamber wherein particles are treated with a liquid, arotatable, helical ribbon disposed in the annular space and having anupright axis of rotation, means for feeding treated particles from theparticle-treating chamber to the'bottom of the helical ribbon, means forrotating the ribbon about its axis to auger upwardly the treatedparticles, with concurrent mixing, within the annular space, and meansfor removing the mixed, treated particles from the top of the ribbon.

2. The apparatus of claim 1 wherein the inner wall is mounted forrotation about the axis of rotation of the helical ribbon and whereinthe helical ribbon is attached to the inner wall for rotation therewith.

3. The apparatus of claim 2 including a floor positioned to receivefallen particles after treatment of the same with a liquid, and meansfor transporting the fallen particles outwardly for reception by thebottom of the helical ribbon.

4. The apparatus according to claim 3 wherein the floor and outer wallare stationary with respect to the inner wall and attached helicalribbon.

5. The apparatus of claim 4 including a power source, a rotatable shaftdriven by the power source and extending upwardly through the floorcoaxial with the axis of rotation of the helical ribbon, and a paddlemounted to the shaft and adapted to sweep fallen treated particles onthe floor outwardly for reception by the bottom of the helical ribbon,the paddle having outwardly extending ends attached to the inner wall,rotation of the shaft causing the paddle, the inner wall, and thehelical ribbon to rotate about the axis of rotation of the latter, thepaddle sweeping fallen particles outwardly of the stationary floor forreception by the bottom of the rotating helical ribbon.

6. The apparatus of claim 5 wherein the annular space between the innerand outer walls houses a plurality of helical ribbons attached to theouter surface of the inner wall, the helical ribbons being helicallyinterlaced to define separate helical passages.

7. The apparatus according to claim 6 wherein the inner wall has a loweredge spaced above the floor to permit outwardly swept treated particlesto pass beneath the lower edge of the inner wall for reception by thebottom of the rotating helical ribbon, the outer wall being rigidlyconnected at its lower edge to the floor, and the paddle ends extendingoutwardly beneath the inner wall and having superior surfaces orientedat an obtuse angle with respect to the floor and which merge intorespective superior surfaces of the lower ends of the helical ribbons.

8. The apparatus according to claim 7 wherein the outer wall has anopening adjacent the upper end of the helical ribbon through whichtreated and mixed particles may pass outwardly of the annular spacebetween the inner and outer walls, each helical ribbon terminatingupwardly in an upright 'deflec'tion plate so oriented as to urgeparticles outwardly so that the 'same may pass through the opening inthe-outer wall for subsequent collection. 7

9. A treating andmixing apparatus for applying a liquid to particles,and mixing the latter, comprising:

a. means for treating particles with a liquid including .a distributingcone having a vertical axis and an upwardly convergent"u-ppe'r'surfacefa chute for dispensing particles onto the 'uppersurface of the cone, the particles falling in a curtain from theperiphery of the cone, and a motor-driven disc rotatably mountedcoaxially below the cone, the disc being adapted to rotate rapidly aboutits axis and to hurl liquid in small droplets outwardly into contactwith the falling curtain of particles;

b. a stationary floor, and an outer, upright, cylindrical wall arisingfrom the floor and having an outward opening adjacent its upper end;

c. a motor-driven, upright shaft extending upwardly through the floorand coaxial with the axis of the cone;

(1. a paddle mounted to the shaft and adapted to rotate therewith tosweep fallen treated particles outwardly toward the outer wall;

e. an inner wall spaced concentrically within the outer wall and mountedto the paddles for rotation about the axis of the cone, the inner wallhaving a bottom edge spaced from the floor, and the floor and inner wallat least partially defining a treatment chamber within which is housedthe cone and disc;

9f. a helical ribbon positioned between the inner and outer walls andmounted to the inner wall for rota tion therewith about the axis of thecone, the ribbon having a bottom end for receiving outwardly sweptparticles from the floor and conveying the particles upwardly withconcurrent mixing, the ribbon terminating at its upper end in a plate sooriented as to deflect the particles laterally outwardly through theopening in the outer wall.

10. The apparatus according to claim 9 wherein the paddle ends extendoutwardly beneath the inner wall, each end having a superior surfaceobtusely angled with respect to the floor and merging with the superiorsurface of the lower end of a helical ribbon so as to deflect particlesfrom the floor upwardly onto the lower end of the helical ribbon.

11. The apparatus of claim 9 wherein the floor and the outer wall areprovided with internal low-friction surfaces.

12. In a treating apparatus for applying a liquid to falling particles,the improvement which comprises a mixer for mixing the treatedparticles, the mixer comprising a pair of concentric, substantiallyvertical cylindrical walls spaced from one another to define an annularspace therebetween, a stationary floor for receiving fallen particlesand attached at its periphery to the outer wall, a helical ribbonmounted within the annular space and attached to the inner wall forrotation therewith, a paddle attached to the inner wall and urgingfallen particles outwardly along the floor'into the annular space forreception by the helical ribbon at its lower end, and means for rotatingthe inner wall and helical ribbon to auger particles upwardly within theannular space with concurrent mixing.

13. In combination with a treating apparatus plying a liquid to fallingparticles, a mixer for mixing the treatedparticl'es, the mixer includingupright, concentric, spaced inner and outer walls defining an annularspace-therebetween, a rotatable, helical ribbon disposed in the annularspace and having gin-upright axis of rotation, the inner wall beingmounted to the helical ribbon for rotation therewith and defining wallsof a central, particle-treating chamber wherein particles are treatedwith a liquid, means for feeding treated particles from theparticle-treating chamber to the bottom of the helical ribbon, meansforrotating the ribbon about its axis to auger upwardly the treatedparticles within the annular space with concurrent mixing of theparticles, and means for removing the mixed, treated particles from thetop of the ribbon.

for ap i 14. A mixerfor mixing particles treated with a liquid, themixer including an upright, stationary, cylindrical outer wall, arotatable inner wall which is concentric with but spaced inwardly of theouter Wall to provide an annular space between the walls, the inner walldefining walls of a central chamber, a rotatable, helical ribbondisposed in the annular space and having an upright axis of rotation,the helical ribbon being attached to the inner wall for rotationtherewith, a stationary floor at the bottom of said chamber and spacedbelow the inner wall for reception of liquid-treated particles, meansfor feeding the fallen treated particles to the bottom of the helicalribbon, and means for rotating the ribbon and inner wall to augerupwardly the treated particles within the annular space for concurrentparticle mixing.

1. In combination with a treating apparatus for applying a liquid tofalling particles, a mixer for mixing the treated particles, the mixerincluding upright, concentric, spaced inner and outer walls defining anannular space therebetween, the inner wall defining walls of a centralparticle-treating chamber wherein particles are treated with a liquid, Arotatable, helical ribbon disposed in the annular space and having anupright axis of rotation, means for feeding treated particles from theparticle-treating chamber to the bottom of the helical ribbon, means forrotating the ribbon about its axis to auger upwardly the treatedparticles, with concurrent mixing, within the annular space, and meansfor removing the mixed, treated particles from the top of the ribbon. 2.The apparatus of claim 1 wherein the inner wall is mounted for rotationabout the axis of rotation of the helical ribbon and wherein the helicalribbon is attached to the inner wall for rotation therewith.
 3. Theapparatus of claim 2 including a floor positioned to receive fallenparticles after treatment of the same with a liquid, and means fortransporting the fallen particles outwardly for reception by the bottomof the helical ribbon.
 4. The apparatus according to claim 3 wherein thefloor and outer wall are stationary with respect to the inner wall andattached helical ribbon.
 5. The apparatus of claim 4 including a powersource, a rotatable shaft driven by the power source and extendingupwardly through the floor coaxial with the axis of rotation of thehelical ribbon, and a paddle mounted to the shaft and adapted to sweepfallen treated particles on the floor outwardly for reception by thebottom of the helical ribbon, the paddle having outwardly extending endsattached to the inner wall, rotation of the shaft causing the paddle,the inner wall, and the helical ribbon to rotate about the axis ofrotation of the latter, the paddle sweeping fallen particles outwardlyof the stationary floor for reception by the bottom of the rotatinghelical ribbon.
 6. The apparatus of claim 5 wherein the annular spacebetween the inner and outer walls houses a plurality of helical ribbonsattached to the outer surface of the inner wall, the helical ribbonsbeing helically interlaced to define separate helical passages.
 7. Theapparatus according to claim 6 wherein the inner wall has a lower edgespaced above the floor to permit outwardly swept treated particles topass beneath the lower edge of the inner wall for reception by thebottom of the rotating helical ribbon, the outer wall being rigidlyconnected at its lower edge to the floor, and the paddle ends extendingoutwardly beneath the inner wall and having superior surfaces orientedat an obtuse angle with respect to the floor and which merge intorespective superior surfaces of the lower ends of the helical ribbons.8. The apparatus according to claim 7 wherein the outer wall has anopening adjacent the upper end of the helical ribbon through whichtreated and mixed particles may pass outwardly of the annular spacebetween the inner and outer walls, each helical ribbon terminatingupwardly in an upright deflection plate so oriented as to urge particlesoutwardly so that the same may pass through the opening in the outerwall for subsequent collection.
 9. A treating and mixing apparatus forapplying a liquid to particles and mixing the latter, comprising: a.means for treating particles with a liquid including a distributing conehaving a vertical axis and an upwardly convergent upper surface, a chutefor dispensing particles onto the upper surface of the cone, theparticles falling in a curtain from the periphery of the cone, and amotor-driven disc rotatably mounted coaxially below the cone, the discbeing adapted to rotate rapidly about its axis and to hurl liquid insmall droplets outwardly into contact with the falling curtain ofparticles; b. a stationary floor, and an outer, upright, cylindricalwall arising from the floor and having an outward opening adjacent itsupper end; c. a motor-driven, upright shaft extending upwardly throughthe floor and coaxial with the axis of the cone; d. a paddle mounted tothe shaft and adapted to rotate therewith to sweep fallen treatedparticles outwardly toward the outer wall; e. an inner wall spacedconcentricAlly within the outer wall and mounted to the paddles forrotation about the axis of the cone, the inner wall having a bottom edgespaced from the floor, and the floor and inner wall at least partiallydefining a treatment chamber within which is housed the cone and disc;9f. a helical ribbon positioned between the inner and outer walls andmounted to the inner wall for rotation therewith about the axis of thecone, the ribbon having a bottom end for receiving outwardly sweptparticles from the floor and conveying the particles upwardly withconcurrent mixing, the ribbon terminating at its upper end in a plate sooriented as to deflect the particles laterally outwardly through theopening in the outer wall.
 10. The apparatus according to claim 9wherein the paddle ends extend outwardly beneath the inner wall, eachend having a superior surface obtusely angled with respect to the floorand merging with the superior surface of the lower end of a helicalribbon so as to deflect particles from the floor upwardly onto the lowerend of the helical ribbon.
 11. The apparatus of claim 9 wherein thefloor and the outer wall are provided with internal low-frictionsurfaces.
 12. In a treating apparatus for applying a liquid to fallingparticles, the improvement which comprises a mixer for mixing thetreated particles, the mixer comprising a pair of concentric,substantially vertical cylindrical walls spaced from one another todefine an annular space therebetween, a stationary floor for receivingfallen particles and attached at its periphery to the outer wall, ahelical ribbon mounted within the annular space and attached to theinner wall for rotation therewith, a paddle attached to the inner walland urging fallen particles outwardly along the floor into the annularspace for reception by the helical ribbon at its lower end, and meansfor rotating the inner wall and helical ribbon to auger particlesupwardly within the annular space with concurrent mixing.
 13. Incombination with a treating apparatus for applying a liquid to fallingparticles, a mixer for mixing the treated particles, the mixer includingupright, concentric, spaced inner and outer walls defining an annularspace therebetween, a rotatable, helical ribbon disposed in the annularspace and having an upright axis of rotation, the inner wall beingmounted to the helical ribbon for rotation therewith and defining wallsof a central, particle-treating chamber wherein particles are treatedwith a liquid, means for feeding treated particles from theparticle-treating chamber to the bottom of the helical ribbon, means forrotating the ribbon about its axis to auger upwardly the treatedparticles within the annular space with concurrent mixing of theparticles, and means for removing the mixed, treated particles from thetop of the ribbon.
 14. A mixer for mixing particles treated with aliquid, the mixer including an upright, stationary, cylindrical outerwall, a rotatable inner wall which is concentric with but spacedinwardly of the outer wall to provide an annular space between thewalls, the inner wall defining walls of a central chamber, a rotatable,helical ribbon disposed in the annular space and having an upright axisof rotation, the helical ribbon being attached to the inner wall forrotation therewith, a stationary floor at the bottom of said chamber andspaced below the inner wall for reception of liquid-treated particles,means for feeding the fallen treated particles to the bottom of thehelical ribbon, and means for rotating the ribbon and inner wall toauger upwardly the treated particles within the annular space forconcurrent particle mixing.